This invention relates in general to spring tighteners and in particular to a new and useful spring tightener for large coil springs especially for motor vehicle axle springs and which includes a telescopic arrangement of the guide tubes for the spring pressure plates.
The invention particularly refers to a spring tightener for large coil springs, especially for motor vehicle axle springs. The device includes two loose, dishlike pressure plates, each with a central insertion opening. The device includes a threaded spindle having a spindle head with key profile, which is mounted by means of an axial thrust bearing revolvingly in a cylindrical guide tube. The bearing is provided with a radial bearing surface to support the pressure plate at the spindle head. Also, cylindrical threaded tube, having an internal threading to screw in the threaded spindle, is firmly joined to and able to move coaxially with the guide tube by a positive-locking guideway and a coupling tube which is provided with a terminal segment having radial fingers about the periphery of the end away from the spindle head. By the engagement of the tube in recesses of the pressure plate away from the spindle head the threaded tube can be brought into a rigid tension coupling with this pressure plate.
In a familiar spring tightener of this kind (German GM 88 26 909.7), the guide tube is joined to the threaded tube by an axially movable multicornered tube with a broken outer rim, such that the threaded tube can telescope into the multicornered tube and the multicornered tube can telescope into the guide tube. The threaded tube can be moved lengthwise in the multicornered tube by means of a suitable multicornered head arranged at the end near the spindle head. The guide tube is provided with an inner multicornered profile at the end away from the spindle head, in which the multicornered tube can be moved lengthwise. Furthermore, at the ends of the multicornered tube and the guide tube away from the spindle head there are snap rings arranged in ring grooves, which serve as axial stops for the multicornered head of the threaded tube and for a head piece at the end of the multicornered tube near the spindle head. In addition, the end of the threaded spindle away from the spindle head is fashioned as a safety ring, and a ring-shaped bearing surface is formed inside the threaded tube by an inwardly projecting interior threading, which forms a stop for the safety ring of the threaded tube in the extended position of the latter. In practice, it has been found that the fabrication of such spring tightener demands relatively high production costs, on account of the multicornered profile that must be used for the torsion protection, and that the interpenetrating tubes are so weakened by the ring grooves necessary to accommodate the snap rings that there is a danger of fracture, given the desire to make the walls as thin as possible.